It is known in the art that alkenyl- or alkyl-substituted succinic anhydrides have been used as dispersants and/or detergents in lubricating oils and fuels. Such alkenyl- or alkyl-substituted succinic anhydrides have been prepared by three well-known processes: a thermal process (see, e.g., U.S. Pat. No. 3,361,673), a chlorination process (see, e.g., U.S. Pat. No. 3,172,892) and a combination of the thermal and chlorination processes (see, e.g., U.S. Pat. No. 3,912,764). The polyisobutenyl succinic anhydride ("PIBSA") produced by the thermal process has been characterized as a monomer containing a double bond in the product. Although the exact structure of chlorination PIBSA has not been definitively determined, the chlorination process PIBSA materials have been characterized as monomers containing either a double bond, a ring other than succinic anhydride ring and/or chlorine in the product. [(See J. Weill and B. Sillion, "Reaction of Chlorinated Polyisobutene with Maleic Anhydride: Mechanism Catalysis by Dichloramaleic Anhydride," Revue de I'Institut Francais du Petrole, Vol. 40, No. 1, pp. 77-89 (January-February, 1985).] Such compositions include one-to-one monomeric adducts (see, e.g., U.S. Pat. Nos. 3,219,666; 3,381,022) as well as "multiply adducted" products, adducts having alkenyl-derived substituents adducted with at least 1.3 succinic groups per alkenyl-derived substituent (see, e.g., U.S. Pat. No. 4,234,435).
Alkenyl or alkyl succinimides formed by the reaction of an alkenyl- or alkyl-substituted succinic anhydride and a polyamine are also well known as lubricating oil dispersant and/or detergent additives. See, e.g., U.S. Pat. Nos. 3,361,673 and 3,018,250.
As taught in U.S. Pat. No. 4,612,132 ("the '132 patent"), alkenyl or alkyl succinimides may be modified such that one or more of the nitrogens of the polyamine moiety is substituted with a hydrocarbyl oxycarbonyl, a hydroxyhydrocarbyl oxycarbonyl or a hydroxy poly(oxyalkylene) oxycarbonyl. These modified succinimides, which impart improved dispersancy and/or detergency properties when employed in lubricating oils, are obtained by reacting the product of an alkyl or alkenyl succinic anhydride and a polyamine with a cyclic carbonate, a linear mono- or poly carbonate, or a chloroformate. The '132 patent discloses succinimide alkenyl or alkyl groups containing from 10 to 300 carbon atoms; most preferred are alkenyl or alkyl groups having from 20 to 100 carbon atoms. However, the highest molecular weight alkenyl or alkyl group specifically taught in the Examples has a molecular weight of 1300. Furthermore, the '132 patent fails to teach anything about the fluoroelastomer seal compatibility of the modified succinimides it discloses.
U.S. Pat. No. 4,747,965 discloses modified succinimides similar to those disclosed in the '132 patent, except that the modified succinimides disclosed in this patent are derived from succinimides having an average of greater than 1.0 succinic groups per alkenyl-derived substituent.
While it is known in the art that succinimide additives useful in controlling engine deposits may be substituted with alkenyl or alkyl groups ranging in number average molecular weight ("Mn") from approximately 300 to 5000, no reference teaches that substituents having a Mn of 2000-2700 perform better than those having a Mn of about 1300. Two references which discuss the effect of the alkenyl-derived substituent's molecular weight on the performance of succinimides as lubricating oil additives are "The Mechanism of Action of Polyisobutenyl Succinimide Lubricating Oil Additives", by E. S. Forbes and E. L. Neustadter (Tribology, Vol. 5, No. 2, pp. 72-77 (April, 1972), and U.S. Pat. No. 4,234,435 ("the '435 patent").
The Forbes and Neustadter article discusses, in part, the effect of polyisobutenyl Mn on the detergency properties of a polyisobutenyl succinimide. However, as shown in FIG. 1 on page 76 of their article, the results of the tests Forbes and Neustadter conducted indicate that succinimides having a 1300 Mn polyisobutenyl substituent are more effective as detergents than those having a polyisobutenyl substituent with a Mn of 2000 or greater. In showing the effect of polyisobutenyl molecular weight on succinimide detergency, this article teaches that maximum detergency performance is obtained when the polyisobutenyl group has a Mn of about 1300.
The '435 patent teaches a preferred polyalkene-derived substituent group with a Mn in the range of 1500-3200. For polybutenes, an especially preferred Mn range is 1700-2400. However, the '435 patent also teaches that the succinimides must have a succinic ratio of at least 1.3, that is at least 1.3 succinic groups per equivalent weight of polyalkene- derived substituent group. Most preferred are succinimides having a succinic ratio of 1.5-2.5. The '435 patent teaches that succinimides must have both a high Mn polyalkylene-derived substituent and a high succinic ratio.
The succinimide additives disclosed in the '435 patent are not only dispersants and/or detergents, but also viscosity index improvers. That is, the '435 additives impart fluidity modifying properties to lubricant compositions containing them. However, viscosity index improving properties are not always desirable for the succinimide, as in the case of single-grade oil formulations, for example. In addition, the succinimide additives disclosed in the '435 patent all contain chlorine, which is undesirable from an environmental point of view.
Polyamino alkenyl or alkyl succinimides and other additives useful as dispersants and/or detergents, such as Mannich bases, contain basic nitrogen. While basicity is an important property to have in the dispersant/detergent additive, it is believed that the initial attack on fluoroelastomer seals used in some engines involves attack by the basic nitrogen. This attack leads to dehydrofluorination, and eventually results in cracks in the seals and loss of other desirable physical properties in the elastomer.
One approach towards solving the elastomer problem is described in U.S. Pat. No. 4,873,009 to Ronald L. Anderson. This patent is also concerned, in part, with the use of succinimides as lube oil additives. Anderson recognizes in Col. 2, lines 28 et seq. that lube additives prepared from "long chain aliphatic polyamines", i.e., succinimides, "are excellent lube oil additives". Anderson teaches such succinimides are "inferior to additives where the alkylene polyamine is hydroxyalkylated" (Col. 2, lines 31-32). Such hydroxyalkylated polyamine- based succinimides, however, "have the drawback that they tend to attack engine seals particularly those of the fluorocarbon polymer type" (Col. 2, lines 35-37).
Anderson solves his fluoroelastomer polymer seal compatibility problem by directly borating his hydroxyalkylated polyamine based succinimides. Furthermore, according to Anderson, it would be desirable for the additive to have a relatively high concentration of N-hydroxyalkyl moieties because the more N-hydroxyalkyl substituents, the cleaner the engine. However, Anderson also teaches that the more amino groups in the polyamine, the greater the degradation of fluoroelastomer seal, and that alkylene amines containing more than 2 amino groups cannot be utilized (Col. 2, lines 50-62).
Accordingly, there exists a need in the art for a succinimide lubricating oil additive which is effective in controlling engine deposits, but which does not require boration to achieve fluoroelastomer seal compatibility.
Coupled with the increasingly severe performance requirements is the issue of heightened environmental concerns. Formulations must therefore avoid the use of potentially harmful elements.
At present, engine oils are formulated to meet the established performance requirements (e.g. API, CCMC, OEM), as well as, satisfying most environmental concerns. But, the removal of elements such as chlorine, and phosphorous have been not been fully achievable.